The present invention relates to an arrangement for transporting air with the aid of so-called ion wind or corona wind.
In principle such an arrangement will include an air flow duct and a corona electrode and a target electrode which are arranged axially spaced from one another in the air flow duct, with the target electrode located downstream of the corona electrode as seen in the desired direction of air flow. Each of the corona electrode and target electrode is connected to a respective terminal of a d.c. voltage source, and the configuration of the corona electrode and the potential difference and distance between corona electrode and target electrode are such as to produce a corona discharge at the corona electrode. This corona discharge gives rise to air ions of the same polarity as the polarity of the corona electrode, and possibly also to electrically charged particles, so-called aerosols, i.e. solid particles or liquid droplets which are present in the air and which are charged electrically by collision with the charged air ions. The air ions migrate rapidly from the corona electrode to the target electrode, under the influence of the electric field, and relinquish their electric charge to the target electrode and return to electrically neutral air molecules. During their passage between respective electrodes, the air ions collide constantly with the electrically neutral air molecules, thereby transferring the electrostatic forces to these latter molecules so that said molecules are also drawn in a direction from the corona electrode to the target electrode, thereby transporting air in the form of a so-called ion wind or corona wind through the air flow duct.
Advantageous embodiments of such air transporting arrangements are described and illustrated in the international patent application PCT/SE85/00538 now U.S. Pat. No. 4,812,711 of Torok et al, issued Mar. 14, 1989.
In air transporting arrangements of this kind it is advantageous, from many aspects, for the corona electrode to be configured in the form of a wire-like electrode element or in the form of a plurality of wire-like electrode elements which are arranged in mutually parallel, adjacent relationship, these wire-like electrode elements being extended across the air flow duct. In this case, the air flow duct will have a rectangular or square cross-sectional shape with two mutually opposing walls which extend parallel with the wire-like corona-electrode elements, and two further walls in which the ends of the wire-like corona-electrode elements are attached in some suitable manner. The number of wire-like electrode elements used in this regard is determined primarily by the width of the air flow duct in a direction perpendicular to the longitudinal extension of the electrode elements, and consequently only a single wire-like electrode element is required in the case of narrow air flow ducts, whereas a wider airflow duct is preferably provided with a multiple of mutually parallel and mutually adjacent wire-like electrode elements.
Certain troublesome problems have been encountered, however, when using a corona electrode which comprises such wire-like electrode elements. As disclosed in the aforementioned international patent application, the efficiency in which the air is transported is directly dependent on the product of the strength of the ion current, i.e. the corona current, and the distance between the corona electrode and target electrode. Furthermore, the ion current should be distributed as uniformly as possible over the whole cross-sectional area of the air flow duct. In the case of a corona electrode which consists of one or more wire-like electrode elements arranged in the aforedescribed manner, it has been found, however, that the duct walls, which normally have an electrically insulated inner surface and an electrically earthed outer surface, and the electrode element attachment means located in said duct walls have a highly significant disturbing effect on the corona discharge which occurs in the proximity of the wire-like electrode elements, and therewith also a significant disturbing influence on the corona current. This screening and disturbing effect necessitates the use of a higher voltage between the corona and target electrodes in order to achieve the corona current desired, and results in uneven distribution of the corona discharge, and therewith the corona current, along the lengths of respective wire-like electrode elements and between the various electrode elements in that case when a plurality of electrode elements are arranged in mutually parallel, side-by-side relationship. When the air transporting arrangement comprises a plurality of mutually parallel and mutually adjacent wire-like electrode elements, these elements will not work under the same conditions, since the outermost electric elements have on one side thereof a wall of the air flow duct, whereas the remaining electrode elements have another wire-like electrode element on either side thereof. It has been found in the case of such arrangements that the various electrode elements are liable to exhibit extreme differences in corona discharge values.